The present invention relates to a light source device for a spectrophotometer to be used as a general-purpose spectrophotometer or a detector of an analytical device such as a liquid-phase chromatograph. Also, the invention relates to a spectrophotometer equipped with the light source device.
A spectrophotometer comprises a light source chamber housing a light source; an optical system for directing light from the light source to a sample; a light detector for detecting light transmitted through the sample; and a light splitter for splitting light directed to the sample or light transmitted through the sample and directed to the detector. A substance has an inherent light absorption coefficient at a specific wavelength. The spectrophotometer identifies a substance from a wavelength that the substance absorbs, or measures a concentration of a substance according to transmittance or absorption of light at a specific wavelength. In a general-purpose spectrophotometer, a liquid sample is placed in a transparent cell, and transmittance of infrared light, visible light, or the like, passing through the cell is measured to analyze the sample. In a liquid-phase chromatograph, a sample flows through a detector from a column, and a spectrophotometer irradiates light on the detector to analyze the sample.
A single light source does not have sufficient light intensity in a wide range from infrared light and visible light to ultraviolet light. Accordingly, the spectrophotometer is normally provided with a heavy hydrogen lamp for generating light mainly in an ultraviolet region and a halogen lamp for generating light in infrared and visible regions. An optical axis is switched to use light from one of the lamps as measurement light (see Patent Document b 1).
A lamp is a heat-generating source as well as a light-emitting source. Accordingly, in the spectrophotometer, the lamp is fixed at a specific position, and is cooled below a specific temperature. Further, the lamp is installed in the spectrophotometer in a state being housed inside a light source chamber, so that a temperature change of a bulb (glass) part is minimized to stabilize light. Cooling air is sent to the light source chamber to be forcibly air-cooled, thereby cooling the lamp housed therein.
The lamp is an expendable part and installed in the light source chamber in a manner so as to be replaceable. FIGS. 4(A) and 4(B) show mechanisms of replacing a lamp in a light source chamber.
As shown in FIG. 4(A), a lamp 2 is inserted into a socket 4, and the socket 4 is installed in an opening at one end of a light source chamber 6. The socket 4 is fixed in the light source chamber 6, and the light source chamber 6 is provided with an opening at an opposite side to the socket 4 for replacing the lamp 2. A lid 8 is detachably attached to the opening, so that the lamp 2 can be replaced by removing the lid 8.
In the light source chamber shown in FIG. 4(A), it is difficult to replace the lamp 2 in a state that the lamp 2 is retained in the light source chamber. Also, it is necessary to touch a bulb part (glass part) of the lamp 2 with a hand, thereby requiring careful handling. If the bulb part is stained, it is possible to deteriorate performance of the lamp.
FIG. 4(B) shows a light source chamber mainly used recently. In the light source chamber, the lamp 2 is fixed to a flange 10, and the flange 10 is detachably attached to an opening of a light source chamber 6a. When the lamp 2 is a heavy hydrogen lamp, a light-emitting part assembly 12 is provided inside the lamp, and heavy hydrogen gas is filled in the lamp at a low-pressure of several Torr. An electrode 14 is connected to the light-emitting part assembly 12, and an electrode support member 14a passes through the flange 10 and extends outside the light source chamber 6a. A window 7 with a transparent window plate fitted therein is formed in the light source chamber 6a for directing light from the lamp 2 to a sample chamber or a light-splitting part.
With the light source chamber shown in FIG. 4(B), it is possible to remove the flange 10 from the light source chamber and take out the flange 10 together with the lamp 2 for replacement without touching the lamp 2, thereby improving handling during replacement of the lamp.
Patent Document 1: Japanese Patent Publication (Kokai) No. 2003-185498
In the light source chamber shown in FIG. 4(B), the bulb part is housed inside the light source chamber 6a. Accordingly, the bulb part does not directly contact the cooling air, thereby preventing a change in the output characteristic due to a temperature change of the bulb part. However, the electrode support part 14a connected to the light-emitting part assembly 12 is exposed outside the light source chamber 6a. Accordingly, the cooling air contacts the electrode support part 14a, and the light-emitting part assembly 12 may be influenced by a temperature via the electrode 14 from the electrode support part 14a, thereby changing the output characteristic.
The cooling air is supplied into the light source chamber 6a from outside the spectrophotometer. When the electrode support part protrudes out from the light-source chamber, the cooling air directly contacts the electrode support part. Accordingly, when the light source is a heavy hydrogen lamp sensitive to a temperature, the lamp is easily influenced by a variation in a room temperature and a flow of the cooling air, thereby changing light intensity and a lighting position of the lamp. As a result, the spectrophotometer may suffer a noise and drift of a baseline of a measurement value such as light absorption.
In view of the problems described above, an object of the present invention is to provide a spectrophotometer with a lamp sensitive to a temperature such as a heavy hydrogen lamp as a light source, in which it is possible to minimize an influence of a temperature on a lamp characteristic.
Further objects and advantages of the invention will be apparent from the following description of the invention.